Cellular communication networks evolve towards higher data rates, together with improved capacity and coverage. In the 3rd Generation Partnership Project (3GPP) standardization body, several technologies have been and are also currently being developed.
LTE (Long Term Evolution) is a recently standardised technology. It uses an access technology based on OFDM (Orthogonal Frequency Division Multiplexing) for the downlink (DL) and Single Carrier FDMA (SC-FDMA) for the uplink (UL). The resource allocation to wireless devices on both DL and UL is performed adaptively using the concept of fast scheduling, taking into account the instantaneous traffic pattern and radio propagation characteristics of each wireless device. Assigning resources in both DL and UL is performed in the scheduler situated in a network node such as the radio base station.
For handling retransmissions of failed Media Access Control (MAC) packets, Hybrid Automatic Repeat Request (HARQ) is used. The HARQ procedure involves providing quick feedback in the form of acknowledgements (ACK) or negative acknowledgements (NACK) to the transmitter for each transport block, depending on the result of the decoding applied at the receiver. HARQ is applied both for downlink transmissions and uplink transmissions.
However, the need for HARQ feedback is increasing, e.g. due to introduction of downlink control transmissions using Enhanced Physical Downlink Control Channel (EPDCCH). Determining the appropriate amount of resources to allocate for HARQ feedback is very difficult. On the one hand, more resources are beneficial to ensure the HARQ feedback is fed back correctly. On the other hand, less resources for HARQ feedback is beneficial to provide more resources for user data.